Optimization of Protein Hydrolysate from Earthworms ( Perionyx excavatus) of Angiotensin-I-Converting Enzyme Inhibitory Activity by One Variable at a Time

Hypertension, characterized by elevated blood pressure, is commonly treated with angiotensin-I-converting enzyme (ACE) inhibitors. This study evaluated the ACE inhibitory activity (ACEIA) of protein hydrolysate from earthworms ( Perionyx excavatus) by commercial proteases. The results showed that the protein hydrolysate of earthworms gave the highestACEIA of 85.38 +/- 2.31% (at the protein concentration of 2 mg/mL) and IC50 value of 844.64 mu g/mL when the earthworms were hydrolyzed with Flavourzyme (R) 500 MG under optimized conditions such as earthworm:phosphate buffer ratio of 1:6 (w/v), hydrolysis temperature of 50 degrees C, pH 7, enzyme:substrate ratio of 600 U/g protein and hydrolysis time of 2 h. The membrane further fractionated the hydrolysate, and the < 1 kDa fraction had the highestACEIA with an IC50 value of 261.94 mu g/mL. The stability of ACEIA was assessed under various conditions, including in vitro digestion, heat treatment at 100 degrees C for 180 min, and pH adjustments from pH 1 to 11. The < 1 kDa fraction maintained ACEIA activity at 133.34, 76.25, and 84.95%, respectively, after these treatments. These results suggest that earthworm protein hydrolysates, particularly the <1 kDa fraction, exhibit strong stability and could be promising candidates for the development of functional foods or pharmaceuticals targeting hypertension.